java md5 加密，转载自：水清云淡

MD5算法称作是散列算法或者称作哈希算法。
MD5是一种单向不可逆的算法，也就是说MD5算法可以用来加密信息内容，但是不能够对经MD5算法加密后的密文进行还原。
MD5算法是能将任意长度的一段信息生成具有固定长度大小的信息摘要，并且该摘要对此信息具有唯一性，那么MD5算法被用于加密信息也是完全可以的，只是不能够对MD5加密后的密文进行还原，毕竟以信息摘要的方式去提取一段信息内容的过程中是有许多有用的重要信息被丢掉了的。


MD5算法比较适用于对字符串做信息摘要，生成具有唯一性且不可逆的密文。
以下是MD5的一种算法：

MD5算法源码：

package com.md5;

public class MD5Encrypt {

	static final int S11 = 7;
    static final int S12 = 12;
    static final int S13 = 17;
    static final int S14 = 22;

    static final int S21 = 5;
    static final int S22 = 9;
    static final int S23 = 14;
    static final int S24 = 20;

    static final int S31 = 4;
    static final int S32 = 11;
    static final int S33 = 16;
    static final int S34 = 23;

    static final int S41 = 6;
    static final int S42 = 10;
    static final int S43 = 15;
    static final int S44 = 21;

    static final byte[] PADDING = { -128, 0, 0, 0, 0, 0, 0, 0, 0,
		    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 
    };
    
    private long[] state = new long[4];  // state (ABCD)
    private long[] count = new long[2];  // number of bits, modulo 2^64 (lsb first)
    private byte[] buffer = new byte[64]; // input buffer
    
    public String digestHexStr;
    
    private byte[] digest = new byte[16];
    
    public String getMD5ofStr(String inbuf) {
    	
        md5Init();
        md5Update(inbuf.getBytes(), inbuf.length());
        md5Final();
        digestHexStr = "";
        for (int i = 0; i < 16; i++) {
                digestHexStr += byteHEX(digest[i]);
        }
        return digestHexStr;

    }
    
    public MD5Encrypt() {
    	
        md5Init();
        return;
    }
    
    private void md5Init() {
        count[0] = 0L;
        count[1] = 0L;
        state[0] = 0x67452301L;
        state[1] = 0xefcdab89L;
        state[2] = 0x98badcfeL;
        state[3] = 0x10325476L;

        return;
    }

    private long F(long x, long y, long z) {
        return (x & y) | ((~x) & z);

    }
    private long G(long x, long y, long z) {
        return (x & z) | (y & (~z));

    }
    private long H(long x, long y, long z) {
        return x ^ y ^ z;
    }

    private long I(long x, long y, long z) {
        return y ^ (x | (~z));
    }
    
    private long FF(long a, long b, long c, long d, long x, long s, long ac) {
        a += F (b, c, d) + x + ac;
        a = ((int) a << s) | ((int) a >>> (32 - s));
        a += b;
        return a;
    }

    private long GG(long a, long b, long c, long d, long x, long s, long ac) {
        a += G (b, c, d) + x + ac;
        a = ((int) a << s) | ((int) a >>> (32 - s));
        a += b;
        return a;
    }
    private long HH(long a, long b, long c, long d, long x, long s, long ac) {
        a += H (b, c, d) + x + ac;
        a = ((int) a << s) | ((int) a >>> (32 - s));
        a += b;
        return a;
    }
    private long II(long a, long b, long c, long d, long x, long s, long ac) {
        a += I (b, c, d) + x + ac;
        a = ((int) a << s) | ((int) a >>> (32 - s));
        a += b;
        return a;
    }
    
    private void md5Update(byte[] inbuf, int inputLen) {

        int i, index, partLen;
        byte[] block = new byte[64];
        index = (int)(count[0] >>> 3) & 0x3F;
        if ((count[0] += (inputLen << 3)) < (inputLen << 3))
             count[1]++;
        count[1] += (inputLen >>> 29);

        partLen = 64 - index;

        if (inputLen >= partLen) {
            md5Memcpy(buffer, inbuf, index, 0, partLen);
            md5Transform(buffer);

            for (i = partLen; i + 63 < inputLen; i += 64) {

                    md5Memcpy(block, inbuf, 0, i, 64);
                    md5Transform (block);
            }
            index = 0;

        } else

            i = 0;

        md5Memcpy(buffer, inbuf, index, i, inputLen - i);

    }
    
    private void md5Final () {
        byte[] bits = new byte[8];
        int index, padLen;

        Encode (bits, count, 8);

        index = (int)(count[0] >>> 3) & 0x3f;
        padLen = (index < 56) ? (56 - index) : (120 - index);
        md5Update (PADDING, padLen);

        md5Update(bits, 8);

        Encode (digest, state, 16);

    }
    
    private void md5Memcpy (byte[] output, byte[] input, int outpos, int inpos, int len) {
        int i;
        for (i = 0; i < len; i++)
            output[outpos + i] = input[inpos + i];
    }
    
    private void md5Transform (byte block[]) {
        long a = state[0], b = state[1], c = state[2], d = state[3];
        long[] x = new long[16];

        Decode (x, block, 64);

        /* Round 1 */
        a = FF (a, b, c, d, x[0], S11, 0xd76aa478L); /* 1 */
        d = FF (d, a, b, c, x[1], S12, 0xe8c7b756L); /* 2 */
        c = FF (c, d, a, b, x[2], S13, 0x242070dbL); /* 3 */
        b = FF (b, c, d, a, x[3], S14, 0xc1bdceeeL); /* 4 */
        a = FF (a, b, c, d, x[4], S11, 0xf57c0fafL); /* 5 */
        d = FF (d, a, b, c, x[5], S12, 0x4787c62aL); /* 6 */
        c = FF (c, d, a, b, x[6], S13, 0xa8304613L); /* 7 */
        b = FF (b, c, d, a, x[7], S14, 0xfd469501L); /* 8 */
        a = FF (a, b, c, d, x[8], S11, 0x698098d8L); /* 9 */
        d = FF (d, a, b, c, x[9], S12, 0x8b44f7afL); /* 10 */
        c = FF (c, d, a, b, x[10], S13, 0xffff5bb1L); /* 11 */
        b = FF (b, c, d, a, x[11], S14, 0x895cd7beL); /* 12 */
        a = FF (a, b, c, d, x[12], S11, 0x6b901122L); /* 13 */
        d = FF (d, a, b, c, x[13], S12, 0xfd987193L); /* 14 */
        c = FF (c, d, a, b, x[14], S13, 0xa679438eL); /* 15 */
        b = FF (b, c, d, a, x[15], S14, 0x49b40821L); /* 16 */

        /* Round 2 */
        a = GG (a, b, c, d, x[1], S21, 0xf61e2562L); /* 17 */
        d = GG (d, a, b, c, x[6], S22, 0xc040b340L); /* 18 */
        c = GG (c, d, a, b, x[11], S23, 0x265e5a51L); /* 19 */
        b = GG (b, c, d, a, x[0], S24, 0xe9b6c7aaL); /* 20 */
        a = GG (a, b, c, d, x[5], S21, 0xd62f105dL); /* 21 */
        d = GG (d, a, b, c, x[10], S22, 0x2441453L); /* 22 */
        c = GG (c, d, a, b, x[15], S23, 0xd8a1e681L); /* 23 */
        b = GG (b, c, d, a, x[4], S24, 0xe7d3fbc8L); /* 24 */
        a = GG (a, b, c, d, x[9], S21, 0x21e1cde6L); /* 25 */
        d = GG (d, a, b, c, x[14], S22, 0xc33707d6L); /* 26 */
        c = GG (c, d, a, b, x[3], S23, 0xf4d50d87L); /* 27 */
        b = GG (b, c, d, a, x[8], S24, 0x455a14edL); /* 28 */
        a = GG (a, b, c, d, x[13], S21, 0xa9e3e905L); /* 29 */
        d = GG (d, a, b, c, x[2], S22, 0xfcefa3f8L); /* 30 */
        c = GG (c, d, a, b, x[7], S23, 0x676f02d9L); /* 31 */
        b = GG (b, c, d, a, x[12], S24, 0x8d2a4c8aL); /* 32 */

        /* Round 3 */
        a = HH (a, b, c, d, x[5], S31, 0xfffa3942L); /* 33 */
        d = HH (d, a, b, c, x[8], S32, 0x8771f681L); /* 34 */
        c = HH (c, d, a, b, x[11], S33, 0x6d9d6122L); /* 35 */
        b = HH (b, c, d, a, x[14], S34, 0xfde5380cL); /* 36 */
        a = HH (a, b, c, d, x[1], S31, 0xa4beea44L); /* 37 */
        d = HH (d, a, b, c, x[4], S32, 0x4bdecfa9L); /* 38 */
        c = HH (c, d, a, b, x[7], S33, 0xf6bb4b60L); /* 39 */
        b = HH (b, c, d, a, x[10], S34, 0xbebfbc70L); /* 40 */
        a = HH (a, b, c, d, x[13], S31, 0x289b7ec6L); /* 41 */
        d = HH (d, a, b, c, x[0], S32, 0xeaa127faL); /* 42 */
        c = HH (c, d, a, b, x[3], S33, 0xd4ef3085L); /* 43 */
        b = HH (b, c, d, a, x[6], S34, 0x4881d05L); /* 44 */
        a = HH (a, b, c, d, x[9], S31, 0xd9d4d039L); /* 45 */
        d = HH (d, a, b, c, x[12], S32, 0xe6db99e5L); /* 46 */
        c = HH (c, d, a, b, x[15], S33, 0x1fa27cf8L); /* 47 */
        b = HH (b, c, d, a, x[2], S34, 0xc4ac5665L); /* 48 */

        /* Round 4 */
        a = II (a, b, c, d, x[0], S41, 0xf4292244L); /* 49 */
        d = II (d, a, b, c, x[7], S42, 0x432aff97L); /* 50 */
        c = II (c, d, a, b, x[14], S43, 0xab9423a7L); /* 51 */
        b = II (b, c, d, a, x[5], S44, 0xfc93a039L); /* 52 */
        a = II (a, b, c, d, x[12], S41, 0x655b59c3L); /* 53 */
        d = II (d, a, b, c, x[3], S42, 0x8f0ccc92L); /* 54 */
        c = II (c, d, a, b, x[10], S43, 0xffeff47dL); /* 55 */
        b = II (b, c, d, a, x[1], S44, 0x85845dd1L); /* 56 */
        a = II (a, b, c, d, x[8], S41, 0x6fa87e4fL); /* 57 */
        d = II (d, a, b, c, x[15], S42, 0xfe2ce6e0L); /* 58 */
        c = II (c, d, a, b, x[6], S43, 0xa3014314L); /* 59 */
        b = II (b, c, d, a, x[13], S44, 0x4e0811a1L); /* 60 */
        a = II (a, b, c, d, x[4], S41, 0xf7537e82L); /* 61 */
        d = II (d, a, b, c, x[11], S42, 0xbd3af235L); /* 62 */
        c = II (c, d, a, b, x[2], S43, 0x2ad7d2bbL); /* 63 */
        b = II (b, c, d, a, x[9], S44, 0xeb86d391L); /* 64 */

        state[0] += a;
        state[1] += b;
        state[2] += c;
        state[3] += d;

    }
    
    private void Encode (byte[] output, long[] input, int len) {
        int i, j;

        for (i = 0, j = 0; j < len; i++, j += 4) {
            output[j] = (byte)(input[i] & 0xffL);
            output[j + 1] = (byte)((input[i] >>> 8) & 0xffL);
            output[j + 2] = (byte)((input[i] >>> 16) & 0xffL);
            output[j + 3] = (byte)((input[i] >>> 24) & 0xffL);
        }
    }

    private void Decode (long[] output, byte[] input, int len) {
        int i, j;
        for (i = 0, j = 0; j < len; i++, j += 4)
            output[i] = b2iu(input[j]) |
                       (b2iu(input[j + 1]) << 8) |
                       (b2iu(input[j + 2]) << 16) |
                       (b2iu(input[j + 3]) << 24);

        return;
    }
   
    public static long b2iu(byte b) {
        return b < 0 ? b & 0x7F + 128 : b;
    }
    
    public static String byteHEX(byte ib) {
        char[] Digit = { '0','1','2','3','4','5','6','7','8','9',
        'A','B','C','D','E','F' };
        char [] ob = new char[2];
        ob[0] = Digit[(ib >>> 4) & 0X0F];
        ob[1] = Digit[ib & 0X0F];
        String s = new String(ob);
        return s;
    }

}

对以上算法生成相应的工具类(方便使用)：

package com.md5;

public class MD5Util {
	
	private static MD5Encrypt MD5 = new MD5Encrypt();
	
	public static String md5Encrypt(String originStr){
		
		return MD5.getMD5ofStr(originStr);
	}
}

接下来新建一个测试类：

package T;

import com.md5.MD5Util;

public class T {

	public static void main(String[] args) {
	
		String test = "123abc";
		System.out.println("MD5加密前：" + test);
		System.out.println("MD5加密后：" + MD5Util.md5Encrypt(test));
	}
}

转载地址：http://fanzhongyun.iteye.com/blog/1221272